J. Org. Chem. 1987,52, 385-390 Partial Conversion of 3a to Its Trans Epimer 5a. After compound 3a had been heated in refluxing ethanol for 48 h, a new, higher running TLC component was detected. Compound 5a and unreacted starting material were isolated after flash column chromatographyof the crude mixture on silica-gel (hexane-EtOAc 4:l) (relative proportions 3a-5a; 3:2). The same results were obtained if compound 3a is treated with a catalytic amount (10%) of ZnBr2 in CH2C12at room temperature for 2 h. 5a (colorlessoil): ‘H NMR (400 MHz, CDCl,) 6 7.30 (m, ArH), 3.63 (dd,J = 6.4 Hz, H-2,6),3.50,3.45 (2 d, JAB= 13 Hz, NCH2CeHS); 13C NMR (CDClJ 6 19.7 (C-4), 29.0 (C-3,5), 50.4 (C-2,6), 58.2 (CHd, 117.0 (CN) 128.4,128.9,129.3, 147.8 (Ar); MS, m / e (relative
385
intensity) 225 (M”, 5), 198 (5))148 (5), 134 (lo), 91 (100). Anal. Calcd for C14H15N3:C, 74.64; H, 6.71; N, 18.65. Found C, 74.35; H, 6.70; N, 17.64. Acknowledgment. We would like to thank Dr. Robert Bucourt for fruitful discussions and Mme. F. Cossart for technical assistance. Supplementary Material Available: Tables of atomic coordinates, thermal parameters, bond distances and angles, and torsional angles (6 pages). Ordering information is given on any current masthead page.
Reactions of Phenylethylenes with O(3P) Atoms in Condensed Phases Elazar Zadok, Sara Rubinraut, and Yehuda Mazur* Department of Organic Chemistry, The Weitmann Institute of Science, Rehooot, Israel
Received February 3, 1986
Oxidation of sytrene, a- and P-alkyl-substituted styrenes,cis- and trans-stilbene,triphenylethylene, allylbenzene, and its trans @alkyl-substitutedderivatives with O(,P) resulted mainly in epoxides and carbonyl compounds formed by 1,2-H shifts. The O(3P) atoms were produced by microwave discharge of 02,COz, or N20/N2in the presence of He. The temperature effect on the relative yields of products was studied on cis-stilbeneand the regioselectivity of the O(3P)attack on the double bond in the series of P-alkylstyrenes and 0-alkyl-substituted allylbenzenes. The mechanism of the oxidation is postulated to involve a diradical intermediate. The temperature effect is explained by the interconversion of different electronic states of this diradical and the steric effect by an early unsymmetric transition state for the addition of O(,P) atoms to the double bond. Oxygen atoms in their ground state [O(3P)atoms] can be formed in several ways, three of which were used for reactions with olefins in the gas phase on a preparative scale: (1)photolysis of N20in the presence of Hg vapors,l (2) microwave discharge of a mixture of O2 and He at low pressures,2 and (3) y-irradiation of substrates dissolved in liquid C02.3 For reactions with olefins in condensed phases, we have utilized the microwave discharge method. We have enlarged its scope using, in addition to 02,C 0 2 and mixtures of N20 and NP4 The technique used by us (1) (a) Cvetanovic,R. J. Adu. Photochem. 1963,1,115. (b) Cvetanovic, R. J.; Ring, D. F.; Doyle, L. C. J . Phys. Chem. 1971, 75, 3056. ( c ) Atkinson, R.iCvetanovic, R. J. J. Chem. Phys. 1971,55,659. (d) Hirokami, S.; Cvetanovic, R. J. J. Am. Chem. SOC.1974,96, 3738. (e) Singleton, D. L.; Cvetanovic, R. J. J. Am. Chem. SOC.1974,96,6812. (0 Gaffney, J. S.; Atkinson, R.; Pitta, J. N., Jr. J. Am. Chem. SOC.1976,98, 1828. (g) Havel, J. J. J. Am. Chem. SOC.1974, 96,530. (h) Havel, J. J.; Chamberlain, W. T.; Krautter, P. M. J. Am. Chem. SOC.1974,96,632. (i) Havel, J. J.; Chan, K. H. J. Org. Chem. 1974,39,2439; J. Am. Chem. SOC.1975, 97, 5800. 6)Havel, J. J. J. Org. Chem. 1978, 43, 762. (2) (a) Bell, A. T. In Techniques and Applications of Plasma Chemistry; Hollahan, J. R., Bell, A. T., Eds.; Wiley-Interdcience: New York, 1974; Chapter 1, pp 1-55. (b) Sato, S.; Cvetanovic, R. J. Can. J. Chem. 1959, 37, 953. (c) Cvetanovic, R. J. Can. J . Chem. 1960, 38, 1678. (d) Huie, R. E.; Herron, J. T. Int. J. Chem. Kinet. 1972, 4, 521. (3) (a) Sakurai, H.; Akimoto, K.; Toki, S.; Takamuku, S. Chem. Lett. 1975,469. (b) Goto, S.; Hori, A.; Takamuku, S.; Sakurai, H. Bull. Chem. SOC.Jpn. 1976,49,2965. (c) Hirokami, S.; Wojnarovita, L.; Sato, S. Bull. Chem. SOC.Jpn. 1979,52,299. (d) Karasawa, H.; Samamoto, T.; Yugeta, R.; Sato, 5.Bull. Chem. SOC.Jpn. 1979,52, 902. (4) (a) Zadok, E.; Amar, D.; Mazur, Y. J. Am. Chem. SOC.1980,102, 6369. (b) Zadok, E.; Sialom, B.; Mazur, Y. Angew. Chem., Int. Ed. Engl. 1980, 19, 1004. (c) Zadok, E.; Mazur, Y. Tetrahedron Lett. 1980,21,4955. (d) Zadok, E.; Mazur, Y. J. Org. Chem. 1982, 47, 2233. (e) Zadok, E.; Rubinraut, S.; Mazur, Y. Isr. J . Chem. 1983, 23, 457. (0 Zadok, E.; Aronovitch, C.; Mazur,Y. N o w . J. Chim. 1982, 6, 699 (9) Zadok, E.; Rubinraut, S.; Frolow, F.; Mazur, Y. J. Am. Chem. SOC.1985,107,2489. (h) Zadok, E.; Rubinraut, S.; Frolow, F.; Mazur, Y. J . Org. Chem. 1985, 50, 2647.
0022-3263/87/1952-0385$01.50/0
is based on microwave discharge of a steady flow of mixtures of gases a t 2-4 torr, which are passed through a U-tube containing the substrates! The “after glow” gases, coming into contact with organic substrates, contain only neutral species, including O(3P)atoms and 02(lAg) molecules. Results This paper describes the reactions of O(3P)with styrene, a- and &substituted styrenes, and allylbenzene and its alkyl derivative^.^ The reactions of styrene, a-substituted styrenes, and cis-stilbene were performed by using the three microwave discharge methods (discharge of 02,C02, or N20/N2in the presence of He), and the reactions of /-?-alkyl styrenes and @-substituted allylbenzenes were carried out by using COz discharge only. This latter method was found to be the simplest and most suitable for preparative uses. The other two methods are less convenient: on O2discharge, the undecomposed O2 molecules may intervene with the reaction course, and the use of N20/N2discharge involves working with a mixture of three gases, which is technically cumbersome. Generally, the reaction was performed on neat liquids (ca. 0.05 mol of substrate) for 30-120 min at variable temperatures. In addition, some reactions were carried out in n-decane solution, in diethylene glycol suspensions, and with substrates in powdered form. The products were also isolated by column chromatography and identified by comparison with authentic samples. cis -Stilbene. The reactions of cis-stilbene (1) were performed by using the three discharge methods which ( 5 ) Part of this work was published as a communication to the Editor, ref 4a.
0 1987 American Chemical Society
Zadok et al.
386 J. Org. Chem., Vol. 52, No. 3, 1987
Table I. Relative Yields ( % ) and Ratios of Products in the Reaction of trans-P-Alkylstyrenes and Allylbenzenes with O(3P) Atoms ratios of products epoxides/ carbonyl cmpds P/h" 2.6 2.5 2.1 3.0
products
carbonyl products
epoxides
substrate 5a 5b 5c 5d
6 61.5
10.5 4 3
8 8 8 15
74 61
1
55
11
59 66
9 3
7
71 70
5e 5f 5g
5h
9
10
20
-
16 10
1 2
2.1
11
5
3
3.0
0.8 0.5
7
32 22
6
1.9
1.8
17
7
9
9
2.1 2.2
1.1 0.4
6 8 13
"Ratios of carbonyl compounds having oxygen at a and (3 positions [(9 + 10)/8] for 5a-d and [9/(8
+ lo)] for 5f-h.
Table 11. Relative Yields (7'0) of Products in the Reaction of Styrene with Different Sources of OPP)Atoms products
, , PhCHz PhCHCH20 CHO
O ( P ) source 1 O2 (15% in He) 2 3 4
COP (15% in He) C 0 2 (5% in He) 5 N2/N20 (6:1, 40% in He) 6 N2/N20 + 02
3-'
20 22
7
13
5
59 62 62 56
28 31 31 25
4
14 9 5
Z
3
5 12
a\ 1 i:
20 4
7 -
I
50
1
50
-s
-_
30 -1nc1
Figure 1. Variation in the amounts of products formed in the reaction of cis-stilbene (1) with O(3P)atoms as a function of (a) time and (b) temperature.
ArCOCHzR +ArCHZCOR+ArCH(R)CHO
0
gave similar results: the formation of cis-stilbene oxide (2), trans-stilbene oxide (31, and benzyl phenyl ketone (4).
I
2 2
products were trans and cis epoxides 6a-d and 7a-d, respectively, and ketones 8a-d and 9a-d, derived from oxygen attack on both CY- and @-olefiniccarbon atoms, respectively (eq 2). In all four reactions, the ratio of ep-
l
I
PhCHO
59
60
co2(100%)
PhCOCH,
'.
At 0 "C, in neat liquid, the conversions were almost complete after 60 min of reaction. The yields of the three products ranged between 70 and 90%, their ratio being independent of the reaction time, indicating that they are primary reaction produds (Figure la). The rest consisted of unidentified insoluble material and traces of diphenylacetaldehyde (
